Complex and interacting biological and biochemical processes are described in terms of mathematical models, (generally complex systems of differential equations) which are studied for their qualitative and quantitative properties. Such results are interpreted to suggest new experiments and to gain insight into the inner workings of systems too complex to examine by laboratory experiments alone. Present applications are to substrate supply within human and/or animal microcirculatory systems; to idealized models of flow in tubes; and to ideal nerve conduction systems.